Since the start of World War I, people have been trying to assist crime fighters with flashlights on their weapons, as may for instance be seem from U.S. Pat. No. 1,149,705, by Eugene S. Ward, issued Aug. 10, 1915 for a Search Light for Firearms.
By contrast, a very sophisticated aiming and target illumination system is seen from U.S. Pat. No. 4,313,272, by John W. Matthews, Ph.D., issued to Laser Products Corporation on Feb. 2, 1982, for Laser Beam Firearm Aim Assisting Methods and Apparatus.
On the more popular level, techniques have developed for the use of hand-held flashlights with firearms.
One such technique has become known as "the Harries technique" that involves holding a handgun with one hand (the "gun hand"), while holding a flashlight with the other hand (the "flashlight hand"), and crossing the "flashlight hand" under the wrist of the "gun hand" for illumination of the target and stabilization of the "gun hand."
Another emerging technique is called "the Rodgers technique" after firearm trainer Bill Rodgers. That Rodgers technique holds the flashlight between the index and middle fingers of the "flashlight hand" and activates the flashlight through an electric tail-end switch which is pressed against the ball of the thumb for illumination of the target, while that "flashlight hand" also steadies the "gun hand."
In order to practise that Rodgers technique, people have put a bicycle innertube over the battery barrel and have used various rubberbands around such barrel in an effort to increase friction and grip by human fingers.